Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
  • B01D67/0081—After-treatment of organic or inorganic membranes
  • B01D67/0083—Thermal after-treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/06—Organic material
  • B01D71/56—Polyamides, e.g. polyester-amides

Definitions

• the invention relates to a semipermeable membrane made from a homogeneously miscible polymer blend and to a process for its production.
• EP-A-0 082 433 gives a clear description of the advantages and disadvantages of already known membranes.
• hydrophilic, asymmetric membranes made from cellulose acetate which have satisfactory antiadsorptive properties, but which leave much to be desired with respect to their thermal and chemical resistance.
• Membranes made from polysulfones or similar polymers may have good thermal and chemical resistance.
• a pronounced tendency in membranes of this type due to the hydrophobic properties of the polymers employed, to adsorb dissolved substances, causing the membrane to become more or less blocked.
• Hydrophilic character and simultaneous resistance to solvents are found in membranes of regenerated cellulose; however, these can be hydrolyzed relatively easily in acidic or alkaline media, and, in addition, they are easily attacked by microorganisms.
• Another object of the present invention is to provide a semipermeable membrane which is stable to hydrolyzing agents and oxidants, is thermally stable, displays improved resistance to organic solvents in comparison to membranes made from a hydrophobic polymer, exhibits low adsorption of proteins, has good wettability, and is insensitive to the action of microorganisms.
• a further object of the present invention is to provide a process for producing the foregoing membrane.
• Yet another object of the present invention is to provide a process for modifying the retention capacity of the foregoing membrane.
• a semipermeable membrane comprising a homogeneously miscible polymer blend which comprises an aromatic polyamide and polyvinyl pyrrolidone.
• the aromatic polyamide is in particular formed of the following general, recurrent structural units of the formula I: ##STR3## wherein E 1 and E 2 are identical or different and are selected from the groupings ##STR4## --Ar 1 --, and --Ar 1 --X--Ar 2 ,
• Ar 1 and Ar 2 are the same or different 1,2-phenylene, 1,3-phenylene or 1,4-phenylene groups which may be substituted by (C 1 -C 6 )-alkyl, (C 1 -C 6 )-alkoxy, --CF 3 or halogen and X denotes
• a process for the production of a membrane as described above which comprises the steps of: providing a solution comprising a solvent and the foregoing homogeneously miscible polymer blend, wherein said solvent comprises an aprotic, polar solvent of the amide type; spreading the solution as a liquid layer on a planar substrate; and applying to the liquid layer a precipitation liquid which is miscible with the solvent of the solution but in which the dissolved homogeneously miscible polymer blend is precipitated as a membrane.
• a process for modifying the retention capacity of a membrane formed by the foregoing process wherein the membrane, in which virtually all the solvent has been replaced by precipitation liquid, is subjected to heat treatment.
• the heat treatment is carried out in a liquid or with steam.
• the aromatic polyamide which is appropriately employed for the membrane according to the invention may be in the form of a random copolymer and also in the form of a block copolymer or a graft copolymer.
• 4,4'-diphenyl sulfone dicarbonyl dichloride 4,4'-diphenyl ether dicarbonyl dichloride, 4,4'-diphenyldicarbonyl dichloride, 2,6-naphthalenedicarbonyl dichloride, isophthaloyl dichloride, but very particularly terephthaloyl dichloride and substituted terephthaloyl dichloride, for example 2-chloroterephthaloyl dichloride.
• Suitable aromatic diamines of the structure H 2 N--Ar 1 --NH 2 comprise m-phenylenediamines or substituted phenylenediamines, for example 2-chlorophenylenediamine, 2,5-dichlorophenylenediamine or 2-methoxy-p-phenylenediamine, in particular p-phenylenediamine.
• Suitable substituted benzidine derivatives include 3,3'-dimethoxybenzidine, 3,3'-dichlorobenzidine, 2,2'-dimethylbenzidine and, preferably, 3,3'-dimethylbenzidine.
• 4,4'-diaminobenzophenone bis(4-aminophenyl)-sulfone, bis[4-(4'-aminophenoxy)phenyl]-sulfone, 1,2-bis(4'-aminophenoxy)-benzene, 1,4-bis[(4'-aminophenyl)isopropyl]-benzene, 2,2'-bis[4-(4'-aminophenoxy)phenyl]-propane, in particular, 1,4-bis-(4'-aminophenoxy)-benzene and mixtures of the diamines mentioned.
• Blends which are advantageously used for preparing preferred embodiments of membranes according to the invention include blends wherein the grouping E 1 comprises identical or different structural units and denotes a 1,3- or 1,4-phenylene group or the group ##STR5##
• Blends wherein the grouping E 2 comprises identical or different structural units and denotes the 1,4-phenylene group or the group ##STR6## wherein R 2 denotes a lower alkyl or alkoxy group having up to 4 carbon atoms each in the alkyl group or F, Cl or Br or the group ##STR7## in which X' is the group --C(R 1 ) 2 --, with R 1 being hydrogen or (C 1 -C 4 ) alkyl, or the grouping ##STR8## are also preferred.
• Blends comprising
• E 1 is a divalent p-phenylene group
• E 2 in the three recurrent structural units is one each of a divalent p-phenylene group, a group of the formula ##STR9## with R 2 being --CH 3 , OCH 3 , F, Cl or Br, and a group of the formula ##STR10## in which X' has the above-indicated meaning, are preferred, as are blends wherein the copolyaramide has the recurrent structural units ##STR11##
• Polyaramides can be prepared in a known manner by solution condensation, interfacial condensation or melt condensation.
• the solution condensation of the aromatic dicarboxylic acid dichlorides with the aromatic diamines is carried out in aprotic, polar solvents of the amide type, such as, for example, in N,N-dimethylacetamide or in particular in N-methyl-2-pyrrolidone.
• aprotic, polar solvents of the amide type such as, for example, in N,N-dimethylacetamide or in particular in N-methyl-2-pyrrolidone.
• halide salts from the first and/or the second group of the periodic table can be added to these solvents in a known manner in order to increase the dissolving power or to stabilize the polyamide solutions.
• Preferred additives are calcium chloride and/or lithium chloride.
• the polycondensation temperatures are usually between about -20° C. and +120° C., preferably between +10° C. and +100° C. Particularly good results are achieved at reaction temperatures between +10° C. and +80° C.
• the polycondensation reactions are preferably carried out in a manner such that about 2 to 30% by weight, preferably 6 to 15% by weight, of polycondensate are present in the solution after completion of the reaction.
• the polycondensation can be stopped in a customary manner, for example by adding monofunctional compounds such as benzoyl chloride.
• the hydrogen chloride which has been produced and is loosely bound to the amide solvent is neutralized by addition of basic substances.
• suitable substances for this purpose are lithium hydroxide and calcium hydroxide, and in particular calcium oxide.
• the Staudinger index is a measure of the mean chain length of the polymers produced.
• the Staudinger index of the membrane-forming aromatic polyamides should be between about 50 and 1,000 cm 3 /g, preferably between 100 and 500 cm 3 /g, particularly preferably between 150 and 350 cm 3 /g. It was determined on solutions each containing 0.5 g of polymer in 100 ml of 96% strength sulfuric acid at 25° C.
• ⁇ 1 viscosity of the pure solvent.
• the blends according to the present invention can be prepared in a customary manner from a common solution of PVP and a polyaramide in an aprotic organic solvent, for example, dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone or N,N-dimethylacetamide.
• aprotic organic solvent for example, dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone or N,N-dimethylacetamide.
• the blends By removing the solvent, e.g. by evaporation, the blends can be isolated and further processed into intermediate products (granules or powder) which can then be used as raw materials for the production of membranes.
• the molecular weight of the PVP is generally about 1,000 to 3,000,000, preferably about 40,000 to 200,000, in particular about 50,000 to 100,000.
• the blends of the present invention are homogeneously miscible in any mixing ratio. They contain, in particular, PVP in quantities ranging from about 1 to 80% by weight, preferably from 5 to 60% by weight and particularly preferably from 10 to 50% by weight, relative to the sum of components (a+b).
• polymer blends described above are not as such the subject matter of the present invention; rather, they are described in detail in connection with moldings, in a patent application of the same priority date. Instead, the invention relates to a semipermeable membrane containing the polymer blend mentioned as the principal component.
• the above-described solution of the blend is filtered and degassed, and a semipermeable membrane is then produced in a known manner by phase inversion (Robert E. Kesting, "Synthetic Polymeric Membranes", 2nd Ed., 1985, p. 237 et seq.).
• the polymer solution is spread as a liquid layer on a substrate which is as planar as possible.
• the planar substrate can comprise, for example, a glass plate or a metal drum.
• a precipitation liquid which is miscible with the solvent of the solution, but in which the polymers dissolved in the polymer solution are precipitated as a membrane is then allowed to act on the liquid layer.
• An example of a precipitation liquid used is water. Due to the action of the precipitation liquid on the liquid layer comprising the polymer solution, the substances dissolved therein precipitate to form a semipermeable membrane.
• the precipitation liquid is advantageously allowed to act on the membrane precipitated thereby until virtually all the solvent has been replaced by precipitation liquid.
• the membrane formed is then freed from precipitation liquid, for example by drying the membrane directly in a stream of air or alternatively by first treating the membrane with a plasticizer, such as glycerol, and then drying it.
• Hollow filaments or capillaries can also be produced in a known manner from the solution of the polymer blend by spinning the polymer solution in accordance with the prior art through an appropriately constructed shaping annular die or hollow-needle nozzle into the precipitation liquid.
• the production conditions can here be chosen in such a way that an external skin or an internal skin or both are formed.
• the wall thickness of capillaries or hollow fibers of this type is usually in the range from about 20 to 500 ⁇ m.
• the membrane is impregnated with glycerol after coagulation, it can preferably contain in the range from about 5 to 60% glycerol, based on its total weight; the membrane impregnated in this way is dried, for example at a temperature of 50° C.
• the membrane according to the invention is likewise suitable as a support membrane for permselective layers produced directly on or in the membrane.
• "ultrathin" layers ⁇ 1 ⁇ m
• functional groups for example silicones, cellulose ethers or fluorinated copolymers
• the membrane according to the invention is also suitable as a support for reactive molecules, for example in order to immobilize enzymes or anticoagulants such as heparin in accordance with the prior art.
• the thickness of the membrane according to the invention without a support layer is in the range from about 10 to 300 ⁇ m, in particular 20 to 120 ⁇ m.
• copolyaramide I was first prepared in N-methylpyrrolidone as solvent from
• TPC terephthaloyl dichloride
• polyaramide II was prepared from about 95 to 100 mol-% of terephthaloyl dichloride and 100 mol-% of bis[4-(4-aminophenoxy)-phenyl]sulfone.
• the membrane properties can subsequently be modified by heat-treating the membrane.
• Examples 2 and 4 it is shown how it is possible to substantially increase the retention capacity for dissolved substances by placing the membrane in hot water (100° C.).
• the Staudinger index for the aromatic polyaramide was determined in 96% strength H 2 SO 4 at 25° C. as specified in the description.
• the mechanical permeability (ultrafiltration) and the retention capacity for dissolved macromolecules were determined in a stirred cylindrical cell (700 rpm, 350 ml, membrane surface area 43 cm 2 ) at pressures of 3.0 bar at 20° C.
• the retention capacity is defined as ##EQU3## C 1 is the concentration of the aqueous test solution, C 2 is the concentration in the permeate.
• test solution employed was a 2% strength aqueous polyvinylpyrrolidone solution (PVP), obtainable under the name "Kollidon K30"® from Messrs. BASF, and the molecular weight of the polyvinylpyrrolidone was 49,000 Daltons.
• PVP polyvinylpyrrolidone solution
• the concentrations were measured in a digital densitometer "DMA 60+601"® from Messrs. Heraeus.
• the membranes of Examples 1 to 3 were placed in acetone for 1 hour in order to replace the liquid present in the membrane pores by acetone.
• the membranes were then exposed to the solvents given in Table 2 for a period of 12 hours at a temperature of 25° C.
• the membranes were then reconditioned to water, and the mechanical permeability and the retention capacity of the membranes treated with the organic solvents were then measured as stated under Example 1.
• the results are given in Table 2 and show that the differences from the values given in Table 1 are within the tolerance limits of the measurement method.
• Aqueous solutions (0.05%) of the colored protein cytochrome C in a stirred cell were subjected to ultrafiltration using the membranes of Examples 1 to 7. After a test period of 30 minutes, the membranes were thoroughly washed with a buffer solution (pH 6.8). The membranes did not show any staining with red cytochrome C, which indicated a low adsorption of proteins.

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• 1989
  • 1989-02-02 DE DE3903098A patent/DE3903098A1/de not_active Withdrawn
• 1990
  • 1990-01-23 CA CA002008328A patent/CA2008328C/en not_active Expired - Fee Related
  • 1990-01-25 DK DK90101455.5T patent/DK0382009T3/da active
  • 1990-01-25 ES ES90101455T patent/ES2071686T3/es not_active Expired - Lifetime
  • 1990-01-25 DE DE59008872T patent/DE59008872D1/de not_active Expired - Fee Related
  • 1990-01-25 EP EP90101455A patent/EP0382009B1/de not_active Expired - Lifetime
  • 1990-01-25 AT AT90101455T patent/ATE120982T1/de active
  • 1990-01-31 KR KR1019900001034A patent/KR0159772B1/ko not_active IP Right Cessation
  • 1990-01-31 NZ NZ232314A patent/NZ232314A/en unknown
  • 1990-01-31 FI FI900483A patent/FI98497C/fi not_active IP Right Cessation
  • 1990-02-01 NO NO900475A patent/NO174375C/no not_active IP Right Cessation
  • 1990-02-01 AU AU49001/90A patent/AU630148B2/en not_active Ceased
  • 1990-02-02 JP JP2024294A patent/JPH03196822A/ja active Pending
• 1991
  • 1991-07-22 US US07/733,377 patent/US5152894A/en not_active Expired - Fee Related

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